Moisture content and joint behavior of bridge decks made of mechanically laminated timber

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University of New Brunswick


Bridges with timber decks are widely used for low-traffic volume areas in New Brunswick, Canada, because of multiple advantages over conventional cast-in-place concrete decks. However, the NLT decks in New Brunswick are required to be replaced every 10-15 years, which is a very costly exercise. This calls for a new type of timber bridge deck system with a service life of more than 15 years. The overall objective of this study was to understand the change in moisture content (MC) of local bridge decks made of nail-laminated timber (NLT), and to develop an improved fastening design for fabricating NLT decks that could provide better structural performance and longer service life. It was found that the MC values varied from 9.9% to 18.2% and 12.8% to 19.7% for Clark Mill Pond over 239 days and for Shikatehawk No.5 over 189 days, respectively. The MC values of timber bridge decks measured during the monitoring period were less than 20%, suggesting that the NLT bridge decks would likely not be prone to rotting caused by biotic attack. The connection tests showed that the connections containing galvanized 80d spiral nails inserted perpendicular to the loading direction and zinc coat partially threaded screws inserted at 45-degree to the loading direction had relatively large stiffness and load capacity values among the nine groups tested, which are recommended for fabricating NLT decks.